Electrosurgical forceps utilize both mechanical clamping action and electrical energy to effect hemostasis by heating the tissue and blood vessels to coagulate, cauterize and/or seal tissue. As an alternative to open forceps for use with open surgical procedures, many modern surgeons use endoscopes, laparoscopes, and endoscopic/laparoscopic instruments for remotely accessing organs through body orifices or smaller, puncture-like incisions. As a direct result thereof, patients tend to benefit from less scarring and reduced healing time.
Laparoscopic instruments are inserted into the patient through a cannula, or port, which has been made with a trocar. Typical sizes for cannulas range from three millimeters to twelve millimeters. Smaller cannulas are usually preferred, which, as can be appreciated, ultimately presents a design challenge to instrument manufacturers who must find ways to make laparoscopic instruments that fit through the smaller cannulas.
Many surgical procedures require cutting or ligating blood vessels or vascular tissue. Due to the inherent spatial considerations of the surgical cavity, surgeons often have difficulty suturing vessels or performing other traditional methods of controlling bleeding, e.g., clamping and/or tying-off transected blood vessels. By utilizing an electrosurgical forceps, a surgeon can cauterize, coagulate/desiccate, and/or simply reduce or slow bleeding simply by controlling the intensity, frequency, and duration of the electrosurgical energy applied through the jaw members to the tissue. Most small blood vessels, i.e., in the range below two millimeters in diameter, can often be closed using standard electrosurgical instruments and techniques. However, if a larger vessel is ligated, it may be necessary for the surgeon to convert the endoscopic procedure into an open-surgical procedure and thereby abandon the benefits of endoscopic surgery. Alternatively, the surgeon can seal the larger vessel or tissue.
It is thought that the process of coagulating vessels is fundamentally different from electrosurgical vessel sealing. For the purposes herein, “coagulation” is defined as a process of desiccating tissue wherein the tissue cells are ruptured and dried. “Vessel sealing” or “tissue sealing” is defined as the process of liquefying the collagen in the tissue so that it reforms into a fused mass. Coagulation of small vessels is sufficient to close them permanently, while larger vessels need to be sealed to assure permanent closure.
To seal larger vessels (or tissue) effectively two predominant mechanical parameters must be accurately controlled—the pressure applied to the vessel (tissue) and the gap distance between the electrodes—both of which are affected by the thickness of the sealed vessel (which term also refers to tissue when used hereinafter and vice versa). More particularly, accurate application of pressure is important to oppose the walls of the vessel, to reduce the tissue impedance to a low enough value that allows enough electrosurgical energy through the tissue, to overcome the forces of expansion during tissue heating, and to contribute to the end tissue thickness, which is an indication of a good seal. It has been determined that a typical fused vessel wall is optimum between 0.001 and 0.006 inches. Below this range, the seal may shred or tear and, above this range, the lumens may not be sealed properly or effectively.
With respect to effective sealing of smaller vessels, the pressure applied to the tissue tends to become less relevant, whereas the gap distance between the electrically conductive surfaces becomes more significant. In other words, the chances of the two electrically conductive surfaces touching during activation increases as vessels become smaller.
Many known instruments include blade members or shearing members that simply cut tissue in a mechanical and/or electromechanical manner and are relatively ineffective for vessel sealing purposes. Other instruments rely on clamping pressure alone to procure proper sealing thickness and are not designed to take into account gap tolerances and/or parallelism and flatness requirements, which are parameters that, if properly controlled, can assure a consistent and effective tissue seal. For example, it is known that it is difficult to adequately control thickness of the resulting sealed tissue by controlling clamping pressure alone for either of two reasons: 1) if too much force is applied, there is a possibility that the two poles will touch and energy will not be transferred through the tissue resulting in an ineffective seal; or 2) if too low a force is applied, the tissue may prematurely move prior to activation and sealing and/or a thicker, less reliable seal may be created.
As mentioned above, to seal larger vessels or tissue properly and effectively, a greater closure force between opposing jaw members is required. It is known that a large closure force between the jaws typically requires a large moment about the pivot for each jaw. This presents a design challenge because the jaw members are typically affixed with pins that are positioned to have small moment arms with respect to the pivot of each jaw member. A large force, coupled with a small moment arm, is undesirable because the large forces may shear the pins. As a result, designers must compensate for these large closure forces by either designing instruments with metal pins and/or by designing instruments that at least partially offload these closure forces to reduce the chances of mechanical failure. As can be appreciated, if metal pivot pins are employed, the metal pins must be insulated to avoid the pin acting as an alternate current path between the jaw members, which may prove detrimental to effective sealing.
Increasing the closure forces between electrodes may have other undesirable effects, e.g., it may cause the opposing electrodes to come into close contact with one another, which may result in a short circuit, and a small closure force may cause premature movement of the tissue during compression and prior to activation. As a result thereof, providing an instrument that consistently provides the appropriate closure force between opposing electrode within a preferred pressure range will enhance the chances of a successful seal. As can be appreciated, relying on a surgeon to manually provide the appropriate closure force within the appropriate range on a consistent basis would be difficult and the resultant effectiveness and quality of the seal may vary. Moreover, the overall success of creating an effective tissue seal is greatly reliant upon the user's expertise, vision, dexterity, and experience in judging the appropriate closure force to seal the vessel uniformly, consistently, and effectively. In other words, the success of the seal would greatly depend upon the ultimate skill of the surgeon rather than the efficiency of the instrument.
A typical operation to uniformly, consistently, and effectively seal and cut vessels with such a device requires the surgeon to perform at least four steps. With the device jaws in the normally open position, the surgeon closes the jaws by actuating a main lever. This lever can have a “ball-point pen” actuation, in that it is a push-to-lock and push-again-to-unlock (or pull-to-lock and pull-again-to-unlock) or it can just be a pull and release lever. With the main lever motion, the jaws close and impart the sealing force to the tissue or vessel. The surgeon, in a second step, presses a button to actuate the electrocautery (signal) and seal the tissue. With appropriate electronic measurements or indicators, the device informs the surgeon when sealing is complete. In a third step, the surgeon pulls a cutting trigger, which physically moves a blade distally to cut the sealed tissue. If the trigger is open-biased (for example, with a spring), it can retract the blade automatically from the tissue when released. If the blade does not stick in the tissue and does retract, the surgeon is required, in a fourth step, to unlock the main lever by pulling it, again, and letting it spring back to its original, open position through the force of a larger bias, such as an another spring, or merely lets it return to the original un-actuated position. If the blade sticks in the extended position, which would prevent the jaws from opening thereafter, a safety device can exist to retract the blade and insure that the jaws can be opened after the surgical procedure is carried out.
It has been found that the pressure range for assuring a consistent and effective seal is between about 3 kg/cm2 to about 16 kg/cm2 and, preferably, within a working range of 7 kg/cm2 to 13 kg/cm2. Manufacturing an instrument that is capable of providing a closure pressure within this working range has been shown to be effective for sealing arteries, tissues, and other vascular bundles.
Various force-actuating assemblies have been developed in the past for providing the appropriate closure forces to effect vessel sealing. For example, one such actuating assembly has been developed by Valleylab Inc., a division of Tyco Healthcare LP, for use with Valleylab's vessel sealing and dividing instrument commonly sold under the registered trademark LIGASURE ATLAS®. This assembly includes a four-bar mechanical linkage, a spring, and a drive assembly that cooperate to consistently provide and maintain tissue pressures within the above working ranges. The LIGASURE ATLAS® is designed to fit through a 10 mm cannula and includes a bi-lateral jaw closure mechanism that is activated by a foot switch. A trigger assembly extends a knife distally to separate the tissue along the tissue seal. A rotating mechanism is associated with distal end of the handle to allow a surgeon to rotate the jaw members selectively to facilitate grasping tissue. Descriptions of such systems and various methods relating thereto can be found in U.S. Pat. Nos. 7,083,618, 7,101,371, and 7,150,749. The contents of all of these applications are hereby incorporated by reference herein.
All of the prior art RF vessel sealing devices require a table-top power-and-signal supply box connected to the electrodes of the jaws through a cumbersome power-and-signal supply line. The supply box takes up precious room within an operating suite. Also, the supply box is expensive to produce, requiring the surgeon/hospital to expend significant amounts of capital to keep the unit on hand. Additionally, the supply line adds cost to produce and maintain. Importantly, the supply line commonly interferes with the surgeon's full freedom of movement during use.
It would be desirable to eliminate the need for large tabletop power supplies and controllers. In particular, it would be desirable to develop a vessel-sealing instrument that is entirely independent of the table-top power-and-signal supply box and the supply line. It would be also desirable to miniaturize the power supply and controllers for the sealing instrument.